ES2711950T3 - Polyethylene composition suitable for film and film applications prepared from it - Google Patents

Abstract

A film comprising a composition of linear low density polyethylene comprising: equal to or less than 100 percent by weight of units derived from ethylene; less than 35 weight percent units from one or more α-olefin comonomers; wherein said linear low density polyethylene composition has a density within the range of 0.890 to 0.915 g/cm3, a molecular weight distribution (Mw/Mn) within the range of 2.5 to 4.5, an index of fluidity (I2) within the range of 3.5 to 8 g/10 minutes, a molecular weight distribution (Mz/Mw) within the range of 2.2 to 3, a vinyl unsaturation of less than 0.1 vinyl per thousand carbon atoms present in the linear low density polyethylene composition and a zero shear viscosity ratio (ZSVR) within the range of 1 to 1.2; where ZSVR is defined as the zero shear viscosity ratio (ZSV) of the branched polyethylene material to the ZSV of the linear polyethylene material at equivalent weight average molecular weight (Mw-gpc) according to the following equation : where the value of Mw-gpc is determined by the conventional GPC method, the value of ZSV is obtained from the creep test by the following method in an ARG2 stress-controlled rheometer (TA Instruments; New Castle , Del) using 25 mm diameter parallel plates at 190°C: the rheometer furnace is set at test temperature for at least 30 minutes before zero setting, at test temperature a molded sample disc is inserted by compression between the plates and allowed to equilibrate for 5 minutes, then lower the top plate to 50 μm above the desired test gap (1.5 mm) while s Adjust any superfluous material and lower the top plate to the desired clearance, carry out measurements under nitrogen purge at a flow rate of 5 L/min (default creep time is set for 2 hours), then a constant low shear stress of 20 Pa is applied to all samples to ensure that the steady state shear rate is sufficiently low in the Newtonian region, while determining the steady state by taking a linear regression for all data in the last 10% of the log (J(t)) vs. log(t) plot time window, where J(t) is the plastic strain compliance and t is the plastic strain time and when If the slope of the linear regression is greater than 0.97, the steady state is considered to have been reached, then the plastic deformation test is stopped and the steady state shear rate is determined from ir of the linear regression slope of all data points in the last 10% of the time window of the plot of ε vs. t, where ε is the stress and the zero-shear viscosity is determined from the ratio of the applied stress to the steady-state shear rate.

Description

DESCRIPTION

Polyethylene composition suitable for film and film applications prepared from it

Field of the invention

The present invention relates to a film comprising a polyethylene composition suitable for film applications.

Background of the invention

It is generally known to use polyethylene compositions in adhesion film applications. Any conventional method, such as a gas phase process, suspension process, solution process or high pressure process, can be used to produce said polyethylene compositions.

Various polymerization techniques have been employed which use different catalyst systems to produce said polyethylene compositions suitable for adhesion film applications.

WO 2009/097222 refers to polyethylene compositions, a method of producing them, articles formed therefrom and a method of preparing them.

Despite research efforts in the development of suitable polyethylene compositions for adhesion film applications, there is still a demand for a polyethylene composition having improved properties such as adhesion strength and minimization of deposition and efflorescence.

Summary of the invention

The present invention provides a film comprising a linear low density polyethylene composition comprising: equal to or less than 10 percent by weight of units derived from ethylene; and less than 35 weight percent of units from one or more α-olefin comonomers; wherein said linear low density polyethylene composition has a density in the range of 0.890 to 0.915 g / cm ³ , a molecular weight distribution (Mw / M n) within the range of 2.5 to 4.5, an index of fluidity (I2) within the range of 3.5 to 8 g / 10 minutes, a molecular weight distribution (Mz / Mw) within the range of 2.2 to 3, vimic unsaturation less than 0.1 vinyls per thousand atoms of carbon present in the linear low density polyethylene composition and a zero shear viscosity ratio (ZSVR) within the range of 1 to 1.2.

Detailed description of the invention

The present invention provides a film comprising a linear low density polyethylene composition comprising: equal to or less than 100 percent by weight of units derived from ethylene; and less than 35 weight percent of units from one or more α-olefin comonomers; wherein said linear low density polyethylene composition has a density in the range of 0.890 to 0.915 g / cm ³ , a molecular weight distribution (Mw / Mn) within the range of 2.5 to 4.5, an index of fluidity (I2) within the range of 3.5 to 8 g / 10 minutes, a molecular weight distribution (Mz / Mw) within the range of 2.2 to 3, a vimic unsaturation of less than 0.1 vinyls per thousand atoms of carbon present in the linear low density polyethylene composition and a zero shear viscosity ratio (ZSVR) within the range of 1 to 1.2.

Low Density Linear Polyethylene Composition

The linear low density polyethylene composition is substantially free of any long chain branching, and preferably, the linear low density polyethylene composition is free of any long chain branching. Substantially free of any long chain branching, as used herein, refers to a linear low density polyethylene composition preferably substituted with less than about 0.1 long chain branches per 1000 total carbons, and more preferably, less than about 0.01 long chain branches per 1000 total carbons.

The term (co) polymerization, as used herein, refers to the polymerization of ethylene and optionally one or more comonomers, for example, one or more α-olefin comonomers. Thus, the term (co) polymerization refers to both polymerization of ethylene and copolymerization of ethylene and one or more comonomers, for example, one or more α-olefin comonomers.

The linear low density polyethylene (LLDPE) composition suitable for the film application (formed by the cast film process) comprises (a) equal to or less than 100 percent, for example, at least 65 percent, at least 75 percent, or at least 80 percent, by weight of units from ethylene; and (b) less than 35 percent, for example less than 25 percent, or less than 20 percent, by weight of units from one or more α-olefin comonomers.

The linear low density polyethylene composition has a density in the range of 0.890 to 0.915 g / cm ³ . All individual values and subintervals from 0.890 to 0.915 g / cm ³ are included and disclosed herein; for example, density can be from a lower Umite 0.890, 0.895, 0.900, 0.902 g / cm ³ to an upper Umite 0.908, 0.910, 0.913 or 0.915 g / cm ^3. For example, the linear low density polyethylene composition may have a density within the range of 0.890 to 0.915 g / cm ³ , or in the alternative, the linear low density polyethylene composition may have a density within the range of 0.895 to 0.913 g / cm ³ , or in the alternative, the linear low density polyethylene composition may have a density within the range of 0.900 to 0.910 g / cm ³ , or in the alternative, the linear low density polyethylene composition may have a density within the range of 0.0902 to 0.908 g / cm ³ .

The linear low density polyethylene composition is characterized by having a zero shear viscosity ratio (ZSVR) within the range of 1 to 1.2.

The linear low density polyethylene composition has a molecular weight distribution (Mw / M n) (measured according to the conventional method of gel permeation chromatography (GPC)) within the range of 2.5 to 4.5. All values and subintervals from 2.5 to 4.5 are included and disclosed herein; for example, the molecular weight distribution (Mw / Mn) can be from a lower limit of 2.5, 2.7, 2.9 or 3.0 to an upper limit of 3.6, 3.8, 3, 9, 4.2, 4.4 or 4.5.

The linear low density polyethylene composition has a flow index (I2) within the range of 3.5 to 8 g / 10 minutes. For example, the fluency index (I2) can be of a lower limit of 3.5 g / 10 minutes at a higher limit of 7.5 to 8 g / 10 minutes.

The linear low density polyethylene composition has a molecular weight (Mw) within the range of 50,000 to 250,000 dalton. All values and subintervals of 50,000 to 250,000 daltons are included and disclosed herein; for example, the molecular weight (Mw) can be from a lower limit of 50,000, 60,000, 70,000 dalton or up to an upper limit of 150,000, 180,000, 200,000 or 250,000 daltons.

The composition of linear low density polyethylene has a molecular weight distribution (Mz / Mw) (measured according to the conventional GPC method) within the range of 2.2 to 3. All individual values and sub-ranges of 2.2 to 3 are included and disclosed herein.

The linear low density polyethylene composition may have a vinyl unsaturation of less than 0.1 vinyls per one thousand carbon atoms present in the linear low density polyethylene composition. All individual values and subintervals of less than 0.1 are included and disclosed herein; for example, the linear low density polyethylene composition may have a vinyl unsaturation of less than 0.08 vinyls per one thousand carbon atoms present in the linear low density polyethylene composition.

The linear low density polyethylene composition may comprise less than 35 weight percent of units from one or more α-olefin comonomers. All individual values and subintervals of less than 35 weight percent are included and disclosed herein; for example, the linear low density polyethylene composition may comprise less than 30 weight percent of units from one or more α-olefin comonomers; or in the alternative, the linear low density polyethylene composition may comprise less than 28 weight percent of units from one or more aolefin comonomers; or in the alternative, the linear low density polyethylene composition may comprise less than 26 percent units from one or more α-olefin comonomers, or in the alternative, the linear low density polyethylene composition may comprise less of 22 weight percent units from one or more α-olefin comonomers.

The linear low density polyethylene composition may comprise at least 12 weight percent of units from one or more α-olefin comonomers. All individual values and sub-ranges from at least 12% by weight are included and disclosed herein. For example, the linear low density polyethylene composition may comprise at least 12 weight percent of units from one or more α-olefin comonomers, or in the alternative, the linear low density polyethylene composition may comprise minus 13 weight percent units derived from one or more α-olefin comonomers; or in the alternative, the linear low density polyethylene composition may comprise at least 14 percent units from one or more α-olefin comonomers.

The α-olefin comonomers typically do not have more than 20 carbon atoms. For example, the α-olefin comonomers may preferably have from 3 to 10 carbon atoms, and more preferably from 3 to 8 carbon atoms. Exemplary α-olefin comonomers include, but are not limited to, propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene and 4-methyl- 1-pentene The one or more aolefin comonomers can be selected, for example, from the group consisting of propylene, 1-butene, 1-hexene and 1-octene; or in the alternative, between the group consisting of 1-hexene and 1-octene.

The linear low density polyethylene composition may comprise less than 65 weight percent of units from one or more α-olefin comonomers. All individual values and subintervals of at least 65 weight percent are included and disclosed herein; for example, the linear low density polyethylene composition may comprise at least 70 weight percent of units derived from ethylene; or in the alternative, the linear low density polyethylene composition may comprise less than one percent by weight of units derived from ethylene; or in the alternative, the linear low density polyethylene composition may comprise less than 74 weight percent of units derived from ethylene, or in the alternative, the linear low density polyethylene composition may comprise less than 78 percent by weight of units from ethylene; or in the alternative, the linear low density polyethylene composition may comprise less than 100 weight percent units derived from ethylene.

The linear low density polyethylene composition may further comprise equal to or less than 100 parts by weight of hafnium residues remaining from the hafnium-based metallocene catalyst per one million parts of the linear low density polyethylene composition. All individual values and subintervals of equal or less than 100 ppm are included and disclosed herein; for example, the linear low density polyethylene composition may further comprise equal to or less than 10 parts by weight of hafnium residues from the hafnium-based metallocene catalyst per one million parts of the linear low density polyethylene composition; or in the alternative, the linear low density polyethylene composition may further comprise equal to or less than 8 parts by weight of hafnium residues remaining from the hafnium-based metallocene catalyst; or in the alternative, the linear low density polyethylene composition may further comprise equal to or less than 6 parts by weight of hafnium residues remaining from the hafnium-based metallocene catalyst for each one million parts of the linear polyethylene composition of low density; or in the alternative, the linear low density polyethylene composition may further comprise equal to or less than 4 parts by weight of hafnium residues remaining from the hafnium-based metallocene catalyst for each one million parts of the linear polyethylene composition of low density; or in the alternative, the linear low density polyethylene composition may further comprise equal to or less than 2 parts by weight of hafnium residues remaining from the hafnium-based metallocene catalyst for each one million parts of the linear polyethylene composition of low density; or in the alternative, the linear low density polyethylene composition may further comprise equal to or less than 1.5 parts by weight of hafnium residues remaining from the hafnium-based metallocene catalyst for every one million parts of the polyethylene composition. linear low density; or in the alternative, the linear low density polyethylene composition may further comprise equal to or less than 1 part by weight of hafnium residues remaining from the hafnium-based metallocene catalyst for each one million parts of the linear polyethylene composition of low density; or in the alternative, the linear low density polyethylene composition may further comprise equal to or less than 0.75 parts by weight of hafnium residues remaining from the hafnium-based metallocene catalyst for every one million parts of the polyethylene composition. linear low density; or in the alternative, the linear low density polyethylene composition may further comprise equal to or less than 0.5 parts by weight of hafnium residues remaining from the hafnium-based metallocene catalyst for every one million parts of the polyethylene composition. linear low density; or in the alternative, the linear low density polyethylene composition may further comprise equal to or less than 0.25 parts by weight of hafnium residues remaining from the hafnium-based metallocene catalyst for every one million parts of the polyethylene composition. linear low density. The remaining hafnium residues from the hafnium-based metallocene catalyst in the linear low density polyethylene composition can be measured by means of x-ray fluorescence (XRF), which is calibrated against the reference standards. Polymeric resin granules were compression molded at elevated temperature to give plates with a thickness of about 3/8 inch (0.95 cm) for the measurement of x-rays in a preferred method. At very low concentrations of the metal, such as below 0.1 ppm, ICP-AES will be an appropriate method for determining the metal residues present in the linear low density polyethylene composition. In one embodiment, the linear low density polyethylene composition substantially lacks chromium, zirconium or titanium, ie, lacks or only, according to what is considered by those skilled in the art, trace amounts of these metals are present. , for example, less than 0.001 ppm.

The linear low density polyethylene composition may further comprise additional additives. Such additives include, but are not limited to, one or more neutralizing agents based on hydrotalcite, antistatic agents, color improvers, colorants, lubricants, fillers, pigments, primary antioxidants, secondary antioxidants, processing aids, UV stabilizers nucleation and combinations thereof. The polyethylene composition of the invention can contain any amounts of additives. The linear low density polyethylene composition may comprise from about 0 to about 10 weight percent combined of said additives, based on the weight of the linear low density polyethylene composition including said additives. All individual values and subintervals from about 0 to about 10 weight percent are included and disclosed herein; for example, the linear low density polyethylene composition may comprise from 0 to 7 weight percent combined additives, based on the weight of the linear low density polyethylene composition including said additives; in the alternative, the linear low density polyethylene composition may comprise from 0 to 5 weight percent combined additives, based on the weight of the linear low density polyethylene composition including said additives; in the alternative, the linear low density polyethylene composition may comprise from 0 to 3 weight percent combined additives, based on the weight of the linear low density polyethylene composition including said additives; in the alternative, the linear low density polyethylene composition may comprise from 0 to 2 weight percent combined additives, based on the weight of the linear low density polyethylene composition including said additives; in the alternative, the linear low density polyethylene composition may comprise from 0 to 1 weight percent combined additives, based on the weight of the linear low density polyethylene composition including said additives; in the alternative, the composition of linear low density polyethylene can comprising from 0 to 0.5 weight percent combined additives, based on the weight of the linear low density polyethylene composition including said additives.

Any conventional ethylene (co) polymerization reaction can be employed to produce said linear low density polyethylene compositions. Said conventional reactions of ethylene (co) polymerization include, but are not limited to, a gas phase polymerization process, a suspension phase polymerization process, a solution phase polymerization process and combinations thereof, which use one or more conventional reactors, for example, fluidized bed gas phase reactors, loop reactors, stirred tank reactors, discontinuous reactors in parallel, series and / or any combination thereof. For example, the linear low density polyethylene composition can be produced by means of a gas phase polymerization process in a single gas phase reactor; however, the production of said linear low density polyethylene compositions is not limited to the gas phase polymerization process, and any of the above polymerization processes may be employed. In one embodiment, the polymerization reactor may comprise two or more reactors in series, parallel or combinations thereof. Preferably, the polymerization reactor is a reactor, for example, a fluidized bed gas phase reactor. In another embodiment, the gas phase polymerization reactor is a continuous polymerization reactor comprising one or more feed streams. In the polymerization reactor, one or more feed streams are combined together, and flowed or cycled continuously through the polymerization reactor by any suitable means. The gas comprising ethylene and optionally one or more comonomers, for example, one or more α-olefins, can be fed through a distributor plate to fluidize the bed in a continuous fluidization process.

In production, a hafnium-based metallocene catalyst system is continuously fed which includes a cocatalyst, as described below with further detail, ethylene, optionally one or more α-olefin comonomers, hydrogen, optionally one or more inert and / or liquid gases, for example, N2, isopentane and hexane, and optionally one or more continuity additives, in a reactor, for example, a fluidized bed gas phase reactor. The reactor may be in fluid communication with one or more discharge tanks, overload tanks, purge tanks and / or recycle compressors. Typically, the reactor temperature is within the range of 70 to 115 ° C, preferably 75 to 110 ° C, more preferably 75 to 100 ° C, and the pressure is within the range of 1.52 to 3.04 MPa (from 15 to 30 atm), preferably from 1.72 to 2.63 (from 17 to 26 atm). A distributor plate in the lower part of the polymeric bed provides a uniform flow of the monomer that flows in an upward direction, the comonomer and the stream of inert gases. A mechanical stirrer may also be provided to provide contact between the solid particles and the comonomer gas stream. The fluidized bed, a vertical cylindrical reactor, may be in the form of a bulb in the upper part to facilitate the reduction of the gas velocity; thereby allowing the granular polymer to separate from the gases flowing upwards. Subsequently, the unreacted gases are cooled to remove the polymerization heat, re-compressed, and subsequently recycled to the bottom of the reactor. Once the residual hydrocarbons have been removed, and the resin is transported under N2 to a purge vessel, moisture can be introduced to reduce the presence of any residual catalyzed reactions with O2 before exposing the linear low density polyethylene composition to oxygen The linear low density polyethylene composition can then be transferred to an extruder for the formation of pellets. Said pellet training techniques are generally known. The linear low density polyethylene composition can be further melt screened. After the melting process in the extruder, the molten composition is passed through one or active mastamices, located in series of more than one, each active sieve having a micrometric retention size of about 2 pm to about 400 pm (from 2 to 4 x 10 '5 m), and preferably from about 2 pm to about 300 pm (from 2 to 3 x 10.5 m), and most preferably from about 2 pm to about 70 pm (from 2 to 7 x 10'6 m), at a mass flow of 1.0 to about 20 kg / s / m2 (from about 5 to about 100 pounds / hour / inch2). Said additional melt screening is disclosed in U.S. Patent No. 6,485,662.

In one embodiment of a fluidized bed reactor, a monomer stream is passed to a polymerization section. The fluidized bed reactor may include a reaction zone in fluid communication with a rate reduction zone. The reaction zone includes a bed of growing polymer particles, polymer particles formed and catalyst composition particles fluidized by means of the continuous flow of polymerizable and modified gaseous components in the form of composition stream and recycle fluid through the reaction zone. Preferably, the composition stream includes a polymerizable monomer, most preferably ethylene and optionally one or more α-olefin comonomers, and may also include condensation agents as is known in the art and is disclosed, for example, in the US Pat. United States No. 4,543,399, United States Patent No. 5,405,922 and United States Patent No. 5,462,999.

The fluidized bed has the general appearance of a dense mass of individually moving particles, preferably polyethylene particles, as generated by gas percolation through the bed. The pressure decrease across the bed is equal to or slightly greater than the weight of the bed divided by the cross-sectional area. In this way, it depends on the geometine of the reactor. To maintain a viable fluidized bed in the reaction zone, the velocity of the surface gas through the bed must exceed the minimum flow required for fluidization. Preferably, the velocity of the surface gas is at least twice the minimum flow velocity. Normally, the surface gas velocity does not exceed 1.5 m / s and normally not more than 0.23 m / s (0.76 ft / s) is sufficient.

In general, the ratio of height to diameter of the reaction zone may vary within the range of about 2: 1 to about 5: 1. The interval, of course, can vary at higher or lower ratios and depends on the desired production capacity. The cross-sectional area of the velocity reduction zone is typically within the range of about 2 to about 3 multiplied by the cross-sectional area of the reaction zone.

The speed reduction zone has an internal diameter larger than the reaction zone, and it may have conical tapered shape. As its name suggests, the speed reduction zone slows the gas velocity due to the increase of the cross-sectional area. This reduction in gas velocity decreases the particles trapped in the bed, reducing the amount of trapped particles that flow from the reactor. The gas that leaves the header area of the reactor is the recycle gas stream.

The recycle stream is compressed in a compressor and then passed through a heat exchange zone that is removed before the current returns to the bed. Typically the heat exchange zone is a heat exchanger, which may be of the horizontal or vertical type. If desired, various heat exchangers may be employed to lower the temperature of the cycle gas stream in stages. It is also possible to locate the compressor downstream of the heat exchanger or at an intermediate point between various heat exchangers. After cooling, the recycle stream is sent back to the reactor through a recycling inlet pipe. The cooled recycle stream absorbs the heat of reaction generated by the polymerization reaction.

Preferably, the recycle stream is sent back to the reactor and to the fluidized bed through a distributor plate. Preferably, a gas baffle is installed at the reactor inlet to prevent the polymer particles present from depositing and agglomerating in a solid mass and to prevent the accumulation of liquid in the lower part of the reactor as well as to facilitate simple transitions between processes that contain liquid in the cycle gas stream and those that do not and vice versa. Such baffles are described in U.S. Patent No. 4,933,149 and U.S. Patent No. 6,627,713.

The hafnium-based catalyst system used in the fluidized bed is preferably stored for service in a container under a gas atmosphere, which is inert to the stored material, such as nitrogen or argon. The hafnium-based catalyst system can be added to the reaction system, or to the reactor, at any time and by any appropriate means, and is preferably added to the reaction system either directly to the fluidized bed or downstream of the last exchanger of heat, that is, the furthest exchanger downstream with respect to the flow, in the recycling line, in which case the activator is fed into the bed or in the recycling line from a dispenser. The hafnium-based catalyst system is injected into the bed at a point above the distributor plate. Preferably, the hafnium-based catalyst system is injected at a point in the bed where good mixing with the polymeric particles takes place. Injection of the hafnium-based catalyst system at any point above the distribution plate facilitates the operation of the fluidized bed polymerization reactor.

Monomers can be introduced into the polymerization zone in various ways including, without limitation, direct injection through a nozzle in the bed or cycle gas line. The monomers can also be sprayed on the upper part of the bed through a nozzle located above the bed, which can contribute to eliminate some drag of fines by the cycle gas stream.

The composition fluid can be fed to the bed through a separate line to the reactor. The composition of the composition stream is determined by means of the gas analyzer. The gas analyzer determines the composition of the recycle stream, and consequently the content of the composition stream is adjusted to maintain a gaseous composition in an essentially stationary state within the reaction zone. The gas analyzer can be a conventional gas analyzer that determines the composition of the recycle stream to maintain the ratios of the components of the feed stream. Said equipment is commercially available from a variety of sources. The gas analyzer is typically located to house the gas from a sampling point located between the speed reduction zone and a heat exchanger.

The production speed of the linear low density polyethylene composition can be controlled appropriately by adjusting the injection rate of the catalyst composition, activator injection or both. Since no change in the injection speed of the catalyst composition modifies the reaction speed and, thus, the speed at which it is generated in the bed, the temperature of the recycle stream entering the reactor is adjusted to cushion any change in the rate of heat generation. This guarantees the maintenance of an essentially constant temperature in the bed. Of course, the complete instrumentation of both the fluidized bed and the cooling system of the recycling stream is useful for detecting any temperature change in the bed that allows the operator or the conventional automated control system to adjust the temperature of the bed properly. recycling stream.

In certain operating conditions, the fluidized bed is maintained at an essentially constant height by removing part of the bed as a product at the rate of formation of the polymer product in the form of particles.

Since the generation speed is directly related to the product formation speed, a measurement of the temperature increase of the fluid through the reactor, that is, the difference between the inlet fluid temperature and the outlet fluid temperature , is indicative of the rate of formation of the linear low density polyethylene composition at a constant fluid velocity if no vaporizable liquid is present, or this is negligible, in the inlet fluid.

In the discharge of the polymeric product in the form of particles from the reactor, it is desirable and preferred to separate the fluid from the product and send the fluid back to the recycling line. There are numerous known ways in the art of achieving this separation. Product discharge systems that can be employed alternatively are disclosed and claimed in U.S. Patent No. 4,621,952. Said system typically employs at least one (parallel) pair of tanks comprising a settling tank and a transfer tank, arranged in series, so that the separated gas phase is sent back from the top of the settling tank to a point in the reactor near the top of the fluidized bed.

In the embodiment of the fluidized bed gas phase reactor, the temperature of the fluidized bed process reactor of the present specification ranges from 70 ° C or 75 ° C or 80 ° C to 90 ° C or 95 ° C or 100 ° C or 110 ° C or 115 ° C, wherein the desired temperature range comprises any upper temperature limit combined with any lower temperature limit described herein. In general, the temperature of the reactor is operated at the highest temperature possible, taking into account the sintering temperature of the polyethylene composition of the invention inside the reactor and the obstruction that may take place in the reactor or in the ( s) recycling line (s).

The above process is suitable for the production of homopolymers comprising units derived from ethylene, or copolymers comprising units derived from ethylene and at least one or more units derived from other α-olefin (s).

In order to maintain a proper catalyst productivity in the present invention, it is preferable that the ethylene is present in the reactor at a partial pressure equal to or greater than 1100 kPa (160 psia) or 1300 kPa (190 psia) or 1380 kPa (200 psia) or 1450 kPa (210 psia) or 1515 kPa (220 psia).

The comonomer, for example one or more α-olefin comonomers, if present in the polymerization reactor, appears in any amount that achieves the desired incorporation of the comonomer weight percentage into the finished polyethylene. This is expressed as ratio in moles of comonomer to ethylene as described herein, which is the ratio of the gas concentration of moles of comonomer in the cycle gas to the concentration of ethylene moles. in the cycle gas. In one embodiment of the production of the polyethylene composition of the invention, the comonomer is present with ethylene in the cycle gas in a molar ratio range of 0 to 0.1 (comonomer: ethylene); and from 0 to 0.05 in another embodiment; and from 0, to 0.04 in another embodiment; and from 0 to 0.03 in another embodiment; and from 0 to 0.02 in another embodiment.

Hydrogen can also be added to the polymerization reactor (s) to control the final properties (e.g., I21 and / or I2) of the linear low density polyethylene composition. In one embodiment, the ratio of hydrogen to total ethylene monomer (ppm H 2 / mole% of C 2) in the flow of circulation gas is within a range of 0 to 60: 1 in one embodiment; from 0.10: 1 (0.10) to 50: 1 (50) in another embodiment; from 0 to 35: 1 (35) in another embodiment; from 0 to 25: 1 (25) in another embodiment; from 7: 1 (7) to 22: 1 (22).

In one embodiment, the production process of the linear low density polyethylene composition comprises the steps of: (1) (co) polymerizing ethylene and optionally one or more α-olefin comonomers in the presence of a hafnium-based metallocene catalyst by means of a process of (co) polymerization in a single stage reactor; and (2) thereby producing the linear low density polyethylene composition.

The hafnium-based catalyst system, as used herein, refers to a catalyst capable of catalyzing the polymerization of ethylene monomers and optionally one or more α-olefin monomers to produce polyethylene. In addition, the hafnium-based catalyst system comprises a hafnocene component. The hafnocene component can comprise hafnium complexes of the mono-, bis- or tricyclopentadienyl type. In one embodiment, the cyclopentadienyl type ligand comprises cyclopentadienyl or isolobal ligands with cyclopentadienyl and substituted versions thereof. Representative examples of isolobal ligands with cyclopentadienyl include, but are not limited to, cyclopentaphenanthrenyl, indenyl, benzindenyl, fluorenyl, octahydrofluorenyl, cyclooctatetraenyl, cyclopentacyclododecene, phenanthreninyl, 3,4-benzofluorenyl, 9-phenyl fluorenyl, 8-H-cyclopen [a] acenaphtenyl, 7H-dibenzofluorenyl, indene [1,2-9] antreno, thiopheenoindenyl, thiophenofluorenyl, hydrogenated versions thereof (e.g., 4,5,6,7-tetrahydroindenyl, or "H4 Ind") and substituted versions thereof. In one embodiment, the hafnocene component is an unsubstituted bis-cyclopentadienyl hafnocene and substituted versions thereof. In another embodiment, the hafnocene component excludes unsubstituted bridged and bridged bis-cyclopentadienyl hafnocenes, and unsubstituted bridged and bridged bis-indenyl hafnocenes. The term "unsubstituted", as used herein, refers to the fact that there are only hydride groups bound to the rings and not another group. Preferably, the hafnocene useful in the present invention may be represented by the formula (in which "Hf" is hafnium):

CpnHfXp (1)

wherein n is 1 or 2, p is 1, 2 or 3, each Cp is independently a cyclopentadienyl ligand or an isolobal ligand with cyclopentadienyl or a substituted version thereof of the ligand to hafnium; and X is selected from the group consisting of hydride, halides, Ci to C10 alkyls and C2 to C12 alkenyls; and wherein when n is 2, each Cp can be linked to one another through a linking group A selected from the group consisting of Ci to C5 alkylene, oxygen, alkylamine, silyl hydrocarbons and siloxyl hydrocarbons. An example of Ci to C5 alkylenes include ethylene bridge groups (-CH2CH2--); an example of the alkylamine linking group includes methylamide (- (CH3) N--); an example of a silyl hydrocarbon linking group includes dimethylsilyl (- (CH3) 2Si-); and an example of a siloxyl-hydrocarbon linking group includes (-O- (CH3) 2Si-O--). In a particular embodiment, the hafnocene component is represented by formula (1), wherein n is 2 and p is 1 or 2.

As used herein, the term "substituted" means that the referenced group possesses at least one moiety instead of one or more hydrogens at any position, the moieties selected from said groups such as halogen radicals such as F, Cl, Br, hydroxyl groups, carbonyl groups, carboxyl groups, amine groups, phosphine groups, alkoxy groups, phenyl groups, naphthyl groups, C1 to C10 alkyl groups, C2 to C10 alkenyl groups and combinations thereof. Examples of substituted aryls and alkyls include, but are not limited to, acyl radicals, alkylamino radicals, alkoxy radicals, aryloxy radicals, alkylthio radicals, carbamoyl radicals, alkyl dialkyl carbamoyl radicals, acyloxy radicals, acylamino radicals, arylamino radicals and combinations of the same. More preferably, the hafnocene component useful in the present invention may be represented by the formula:

(CpR ⁵ ) ² HfX ² (2)

wherein each Cp is a cyclopentadienyl ligand and each is linked to hafnium; each R is independently selected from hydrides and C1 to C10 alkyls, most preferably hydrides and C1 to C5 alkyls; and X is selected from the group consisting of hydride, halide, C1 to C10 and alkenyl C2 to C12, and more preferably X is selected from the group consisting of halides, alkylenes C2 to ^C6 and C1 to Ca, and most preferably X is selected from the group consisting of chloride, fluoride, C1 to C5 alkyls and C2 alkylenes to Ca. In the most preferred embodiment, the hafnocene is represented by formula (2) above, wherein at least one R group is an alkyl as defined above, preferably a C1 to C5 alkyl, and the others are hydrides. In the most preferred embodiment, each Cp is independently substituted with one, two or three groups selected from the group consisting of methyl, ethyl, propyl, butyl and isomers thereof.

In one embodiment, the hafnocene-based catalyst system is heterogeneous, i.e., the hafnocene-based catalyst may further comprise a support material. The support material can be any material known in the art of supporting catalyst compositions; for example an inorganic oxide; or in the alternative, silica, alumina, silica-alumina, magnesium chloride, graphite, magnesia, titania, zirconia and montmorillonite, any of which may be chemically / physically modified such as by means of fluorination, calcination or other processes. known in the art. In one embodiment, the support material is a silica material having an average particle size, as determined by means of Malvem analysis of 1 to 60 mm; or in the alternative, from 10 to 40 mm.

The hafnium-based catalyst system may also comprise an activator. Any suitable activator known to activate the catalyst components against the polymerization of olefins may be appropriate. In one embodiment, the activator is alumoxane; in the alternative, metalumoxane as described by J. B. P. Soares and A. E. Hamielec in 3 (2) POLYMER REACTION ENGINEERING 131 200 (1995). Preferably, the alumoxane can be co-supported on a support material in a molar ratio of aluminum to hafnium (Al: Hf) ranging from 80: 1 to 200: 1, most preferably from 90: 1 to 140: one.

Such hafnium-based catalyst systems are further described in more detail in U.S. Patent No. 6,242,545 and U.S. Patent No. 7,078,467.

End use applications

The polyethylene composition can be used in adhesion film applications, for example, in adhesion film film applications, for example, for industrial packaging applications and / or food packaging applications.

The present invention provides a film comprising a linear low density polyethylene composition comprising: equal to or less than 100 percent by weight of units derived from ethylene; and less than 35 weight percent of units from one or more α-olefin comonomers; wherein said linear low density polyethylene composition has a density in the range of 0.890 to 0.915 g / cm ³ , a molecular weight distribution (Mw / Mn) within the range of 2.5 to 4.5, an index of fluidity (I2) within the range of 3.5 to 8 g / 10 minutes, a molecular weight distribution (Mz / Mw) within the range of 2.2 to 3, a vimic unsaturation of less than 0.1 vinyls per thousand atoms carbon present in the main chain of said composition and a zero shear viscosity ratio (ZSVR) within the range of 1 to 1.2.

A method of forming an article is provided comprising the steps of: (1) selecting a linear low density polyethylene composition comprising: equal to or less than 100 percent by weight of units derived from ethylene; and less than 35 weight percent of units from one or more comonomers of α-olefin; wherein said linear low density polyethylene composition has a density in the range of 0.890 to 0.915 g / cm3, a molecular weight distribution (Mw / Mn) within the range of 2.5 to 4.5, an index of fluidity ( I2) within the range of 2 to 10 g / 10 minutes, a molecular weight distribution (Mz / Mw) within the range of 2.2 to 3, a vinyl unsaturation of less than 0.1 vinyls per thousand carbon atoms present in the main chain of said composition and a zero shear viscosity ratio (ZSVR) within the range of 1 to 1.2; (2) forming said linear low density polyethylene composition to give rise to one or more layers of adhesion film by means of a film processing technique selected from the group consisting of extrusion molding and molding film techniques. blown (4) thereby forming a packaging device.

In an alternative embodiment, the polyethylene composition improves the strength of adhesion performance. In another alternative embodiment, the polyethylene composition minimizes deposition and efflorescence during extrusion molding. In another alternative embodiment, the polyethylene composition provides an adhesion film with improved adhesion to pale performance.

The compositions can be used in various packages, for example in industrial packaging applications or in food packaging applications.

In the extrusion process of molded film, one or more films are subjected to extrusion through one or more slits on a highly polished and cooled rotating roller, where the one or more films are cooled on one side. The speed of the roller controls the stretching ratio and the final film thickness. Subsequently, the film is sent to a second roller for cooling on the other side. Finally, it passes through a roller system and is rolled into a roll.

In a blown film process, one or more layers of molten polymers are extruded through an annular die, the molten polymer tube is pulled by means of a pair of press rolls above the nozzle and at the same time The fine air that comes out of the air rings enflames and freezes the film as it travels upwards. The speed of the pressure rollers controls the stretching ratio and the final thickness of the film. The pressure rollers flatten the tube to give a double layer of film that can be rolled up later in a roll.

Examples

The following examples are not intended to limit the scope of the invention. The examples of the present invention possess improved adhesion properties.

Composition 1 Linear Low Density

The linear composition 1 of low density (LLDPE-1) is an ethylene-hexene interpolymer, having a density of about 0.904 g / cm 3, an index of fluidity (I 2), measured at 190 ° C and 2.16 kg, of approximately 4 g / 10 minutes, a flow relation (I21 / I2) of approximately 27.

LLDPE-1 can be prepared by means of gas phase polymerization in an individual fluidized bed reactor system in the presence of a hafnium-based catalyst system, as described above, represented by means of the following structure:

Composition 2 Linear Low Density

The linear composition 2 of low density (LLDPE-2) is an ethylene-hexene interpolymer, having a density of about 0.904 g / cm 3, an index of fluidity (I 2), measured at 190 ° C and 2.16 kg, of approximately 7 g / 10 minutes, a flow relation (I21 / I2) of approximately 27.

LLDPE-2 can be prepared by means of gas phase polymerization in an individual fluidized bed reactor system in the presence of a hafnium-based catalyst system, as described above, represented by means of the following structure:

Test methods

These methods include the following:

fluency fodice

The flow rates were measured (I2 and I21) in accordance with ASTM D-1238 at 190 ° C and 2.16 kg and 21.6 kg load, respectively. Their values are presented in g / 10 minutes.

Density

Samples were prepared for density measurement according to ASTM D4703. The measurements were carried out in one hour from the sample pressing using ASTM D792, Method B.

Dynamic shear rheology

The samples were compression molded to give circular plates 25 mm in diameter and 3 mm thick, at 177 ° C for 5 minutes under a pressure of 10 MPa in air. Next, the samples were taken out of the press and placed in the counter for cooling.

Measurements of constant temperature frequency deviation were carried out on an ARES tension controlled rheometer (TA Instruments) equipped with 25 mm parallel plates, under nitrogen purge. For each measurement, the rheometer was thermally balanced for at least 30 minutes before zeroing the separation. The sample was placed on the plate and allowed to melt for five minutes at 190 ° C. Subsequently, the plates were cooled down to 2 mm, the sample was adjusted and then the test was started. The method has an additional delay accumulation of five minutes, to allow temperature equilibrium. The experiments were carried out at 190 ° C over a frequency range of 0.1-100 rad / s at five points for each decade interval. The voltage amplitude was constant at 10%. The voltage response in terms of phase amplitude was analyzed, from which the storage module (G '), loss modulus (G "), complex module (G *), dynamic viscosity (n *) were calculated. and tan (8) or tan delta.

Melt Strength

The melt strength measurements were carried out in a Gottfert Rheotens 71.97 (Goettfert Inc., Rock Hill, SC) linked to a Gottfert Rheotester 2000 capillary rheometer. A polymer melt is extruded through a nozzle. capillary with a flat entry angle (180 degrees) with a capillary diameter of 2.0 mm and an aspect ratio (capillary length / capillary diameter) of 15.

After equilibrating the samples at 190 ° C for 10 minutes, the piston is operated at a constant piston speed of 0.265 mm / s. The temperature of the conventional test is 190 ° C. The sample is extracted uniaxially to a set of acceleration rollers located 100 mm below the nozzle with an acceleration of 2.4 mm / s2. The traction force is recorded as a function of the pickup speed of the pressure rollers. The melt strength is presented as the plateau force (cN) before the break of the strand. The following conditions are used in melt strength measurements: Plunger speed = 0.265 mm / s; wheel acceleration = 2.4 mm / s2; capillary diameter = 2.0 mm; capillary length = 30 mm; and container diameter = 12 mm.

High Temperature Gel Permeability Chromatography

The Gel Permeability Chromatography (GPC) system consists of a 150C high temperature chromatograph (Milford, Mass) from Waters (other suitable high temperature GPC instruments include Polymer Laboratories (Shropshier, UK) Model 210 and Model 220) equipped with a functional differential refractometer (RI) (other appropriate concentration detectors may include an IR4 infrared detector from Polymer ChAR (Valencia, Spain)). The data collection is carried out using a Viscotek TriSEC, Version 3, and a Viscotek 4-channel DM400 Data Manager. The system is also equipped with a solvent degassing device in line from Polymer Laboratories (Shropshire, United Kingdom).

Appropriate high temperature GPC columns can be used such as four columns of 13 micrometres Shodex HT803 of 30 cm length or four columns of 30 cm length of Polymer Labs of mixed pore size fill of 20 micrometers (MixA LS, Polymer Labs). The sample carousel compartment is operated at 140 ° C and the column compartment is operated at 150 ° C. The samples are prepared at a concentration of 0.1 grams of polymer in 50 milliliters of solvent. The chromatographic solvent and the preparation solvent of sample contains 200 ppm of trichlorobenzene (TCB). Both solvents are run with nitrogen. The polyethylene samples are stirred vigorously at 160 ° C for four hours. The injection volume is 200 microliters. The flow rate through GPC is 1 ml / minute.

The GPC column set is calibrated by operating 21 polystyrene patterns of narrow molecular weight distribution. The molecular weight (MW) of the standards ranges from 580 g / mol to 8,400,000 g / mol, and the standards are incorporated in 6 cocktail mixes. Each pattern mixture has at least a decade of separation between the individual molecular weights. Pattern blends are purchased from Polymer Laboratories. The polystyrene standards are prepared at 0.025 g in 50 ml of solvent for molecular weights equal to or greater than 1,000,000 g / mol and 0.05 g in 50 ml of solvent for molecular weights less than 1,000,000 g / mol. The polystyrene standards were dissolved at 80 ° C with intense agitation for 30 minutes. Mixtures of narrow standards are first operated in order to decrease the higher molecular weight component to minimize degradation. The maximum molecular weights of the polystyrene standard are converted to polyethylene molecular weight using the following equation (as described in Williams and Ward, J. Polym, Sci., Polym, Letters, 6, 621 (1968)):

Mpolyethylene _ A X (Mpolystyrene) B,

where M is the molecular weight of polyethylene or polystyrene (as shown) and B equals 1.0. It is known to those skilled in the art that A may be within the range of about 0.38 to about 0.44 and is determined at the time of calibration using a broad polyethylene pattern.

Method of Measurement of Null Shear Viscosity by Plastic Deformation

The zero shear viscosities are obtained by means of plastic deformation tests which were carried out in a tension controlled rheometer AR-G2 (TA Instruments, New Castle, Del) using parallel plates of 25 mm diameter at 190 ° C. The rheometer oven is set to a test temperature for at least 30 minutes before the zero setting. At the test temperature, a sample disk molded by compression is inserted between the plates and allowed to reach equilibrium for 5 minutes. Subsequently, the upper plate is lowered to 50 μm above the desired test gap (1.5 mm). Any superfluous material is adjusted and the top plate is lowered to the desired separation. Measurements are made under nitrogen purge at a flow rate of 5 l / min. The plastic deformation time is adjusted by default for 2 hours.

A constant tension of low shear of 20 Pa is applied for all the samples in order to guarantee that the steady state shear rate is sufficiently low to be in the Newtonian region. The resulting shear rates at steady state are within the range of 10 ^-3 to 10 ^-4 s ^-1 for the samples of the present study. The steady state is determined by taking the linear regression for all the data in the last 10% of the time window of the log diagram (J (t)) vs log (t), where J (t) is the compliance of plastic deformation and t It is the time of plastic deformation. If the slope of the linear regression is greater than 0.97, it is considered that the steady state has been reached, then the plastic deformation test is stopped. In all cases in the present study, the slope meets the criterion in 2 hours. The steady-state shear rate is determined from the slope of the linear regression of all data points in the last 10% of the time window of the diagram of £ vs t, where £ is tension. The zero shear viscosity is determined from the ratio of the stress applied to the steady state shear rate.

In order to determine if the sample is degraded during the plastic deformation test, a small amplitude oscillatory shear test is carried out before and after the plastic deformation test on the test sample from 0.1 to 100 rad / s. The complex viscosity values of the two tests are compared. If the difference of the viscosity values at 0.1 rad / s is greater than 5%, it is considered that the sample has been degraded during the plastic deformation test and the result is discarded.

Null Shear Viscosity Ratio (ZSVR) is defined as the zero shear viscosity ratio (ZSV) of the branched polyethylene material with respect to ZSV of the linear polyethylene material at the average molecular weight expressed in equivalent weight (Mw-gpc) of according to the following equation:

The value of ZSV is obtained from the plastic deformation test at 190 ° C by means of the method described above. The value of Mw-gpc is determined by means of the conventional GPC method. The correlation between ZSV of linear polyethylene and its Mw-gpc was established based on a series of linear polyethylene reference materials. A description of the ZSV-Mw relationship can be found in the previous ANTEC: Karjala, Teresa P .; Sammler, Robert L .; Mangnus, Marc A .; Hazlitt, Lonnie G .; Johnson, Mark S .; Hagen, Charles M., Jr .; Huang, Joe WL; Reichek, Kenneth N. Detection of low levels of long-chain branching in polyolefins. Annual Technical Conference - Society of Plastics Engineers (2008), 66a 887-891.

Vílica Insaturation

The level of vimic unsaturation is determined by means of FT-IR (Nicolet 6700) in accordance with ASTM D6248-98.

Test conditions of PeKcula

The following physical properties are measured in the films produced:

Total Brightness: For the measurement of total brightness, samples are taken and prepared according to ASTM D 1746. A Hazegard Plus (BYK-Gardner USA, Columbia, MD) is used for the assay.

45 ° brightness: ASTM D-2457.

Transparency: Transparency is measured in accordance with ASTM D-1746.

Tear Resistance of Elmendorf in MD and CD: ASTM D-1922.

Impact Resistance with Dart: ASTM D-1709, Method A.

Adhesion on Pale: Adhesion on pale was measured using a Lantech SHS test kit. The test consists of stretching the film at a stretch of 250% at a constant F2 of 10 pounds for 5 turns, operating the rotary table at a speed of 10 rpm. Subsequently, the final end of the film is attached to a load cell that measures the amount of force, in grams, necessary to remove the film from the drum. Three replicas are carried out, presenting the average value as a result of adhesion.

Claims (1)

1. A cell comprising a linear low density polyethylene composition comprising: equal to or less than 100 weight percent of units derived from ethylene; less than 35 weight percent of units from one or more α-olefin comonomers; wherein said linear low density polyethylene composition has a density within the range of 0.890 to 0.915 g / cm ³ , a molecular weight distribution (Mw / Mn) within the range of 2.5 to 4.5, an index of fluidity (I2) within the range of 3.5 to 8 g / 10 minutes, a molecular weight distribution (Mz / Mw) within the range of 2.2 to 3, a vinicidal unsaturation less than 0.1 vinyls per one thousand carbon atoms present in the linear low density polyethylene composition and a zero shear viscosity ratio (ZSVR) within the range of 1 to 1.2; wherein ZSVR is defined as the zero shear viscosity ratio (ZSV) of the branched polyethylene material with respect to the ZSV of the linear polyethylene material at the average molecular weight expressed in equivalent weight (Mw-gpc) according to the following equation : ZS J ^ R. ______ VoB ? / or £ 2.29 3.65 "15M w-gpc in which the value of Mw-gpc is determined by means of the conventional GPC method, the value of ZSV is obtained from the plastic deformation test by means of the following method in a voltage controlled rheometer AR-G2 (TA Instruments; New Castle, Del) using parallel plates of 25 mm diameter at 190 ° C: the remeter furnace is set at a test temperature for at least 30 minutes before the fixings to zero, at the test temperature a disc is inserted sample is molded by compression between the plates and allowed to reach equilibrium for 5 minutes, then the top plate is lowered to 50 ^ m above the desired test gap (1.5 mm) while adjusting any superfluous material and the upper plate is lowered to the desired separation, the measurements are carried out under nitrogen purge at a flow rate of 5 l / min (the plastic deformation time is adjusted by default for 2 hours), subsequently a a constant tension at low shear of 20 Pa for all samples in order to guarantee that the steady state shear rate is sufficiently low in the Newtonian region, while the steady state is determined by taking a linear regression for all the data in the last 10% of the time window of the log diagram (J (t)) vs log (t), where J (t) is the compliance of the plastic deformation and t is the plastic deformation time and when the slope of the linear regression is greater than 0.97, it is considered that the steady state has been reached, then the plastic deformation test is stopped and the shear rate in the steady state is determined from the linear regression slope of all the data points in the last 10% of the time window of the £ vs. diagram t, where £ is the tension and the zero shear viscosity is determined from the ratio of the stress applied to the shear rate in the steady state.